PROJECT SUMMARY Multiple organ dysfunction syndrome (MODS), the concurrent dysfunction of two or more organ systems, results from critical illness or injury. Among hospitalized children and adults, the acquisition of MODS is associated with significant in-hospital morbidity and mortality. Whereas studies among adults have reported a significant toll inflicted by critical illness on long-term outcomes and health resource use, there is a paucity of information on the impact of MODS on the long term survival and functional outcomes of children, and the long-term economic burden that accrues from MODS. It is also unknown how long MODS persists in children beyond their initial hospitalization, and what the associated burden might be in terms of organ-supportive technology-dependent care over time. Given the projected long life span of children and declining in-hospital mortality over time among critically ill or injured children, there is urgent need for improved understanding of the long term sequelae of pediatric critical illness among survivors, measured in terms of residual morbidity, premature mortality, and the health care costs that accrue over time. Among critically ill or injured children initially hospitalized with MODS, the proposed project aims to: (1) assess the enduring morbidity after the hospitalization for MODS, measured in terms of emergency department (ED) visits and re-hospitalizations; (2) measure the costs of care associated with MODS over time; (3) measure the mortality attributable to MODS beyond the initial hospitalization; and (4) compare post-hospitalization morbidity, costs of care, and mortality between different causes of MODS to identify modifiable targets for reduction of the burden associated with MODS. To execute this study, two cohorts of children will be identified within a large, geographically diverse, nationwide claims database: a cohort of hospitalized critically ill children with MODS and a separate cohort of hospitalized critically ill children without MODS but with similar pre-hospitalization comorbidities and the same diagnoses as the children with MODS. Robust longitudinal data analytical techniques will: (1) compare the frequency of ED visits and re-hospitalizations between the two cohorts for up to five years after the initial hospitalization; (2) compare the total costs of care between the two cohorts for up to five years after the initial hospitalization; (3) compare post-hospitalization mortality between the two cohorts; and (4) compare post- hospitalization mortality, frequency of ED visits, re-hospitalizations, and costs of care between the different etiologies of MODS. The study will be the first to highlight the long term morbidity and economic burden that accrue from MODS in children. It will also highlight etiology-specific variation in these long-term sequelae of MODS, thereby providing opportunities for targeted efforts to enhance healthcare delivery systems that ensure care for pediatric MODS is optimal, efficient, and effective in the hospital setting and beyond.